Many crops set fruit within a particular range of temperatures and under certain environmental conditions. Beyond this range of temperatures and environmental conditions, fruit typically does not set because of the lack of production of sufficient amounts of fertile pollen and difficulties in pollination and fertilization. For example, tomatoes set fruit in a narrow range of temperatures of 15.degree. to 21.degree. C. (night) and 30.degree. to 35.degree. C. (day). A. N. Lukyanenko, "Parthenocarpy in Tomato," Monographs on Theoretical and Applied Genetics 14, pgs. 167-177 (1991).
Parthenocarpy is the production of fruit without fertilization. Certain environmental conditions favor parthenocarpy such as high or low temperatures day or night, low light intensity, and high humidity. Parthenocarpy may be induced artificially or may occur naturally. In induced parthenocarpy, various growth regulators can be used to facilitate fruit setting. For example, auxins are commonly applied to facilitate fruit setting in tomato (Lycopersicon esculentum) grown during winter-spring on the Mediterranean coast.
Natural or genetic parthenocarpy may be obligate or facultative. Obligative parthenocarpy results from genetic sterility, arises without any external stimulation, and requires a vegetative method of propagation. Obligative parthenocarpy is found in such fruits as the banana and pineapples A. N. Lukyanenko, "Parthenocarpy in Tomato," Monographs on Theoretical and Applied Genetics 14, pgs. 167-177 (1991). Facultative parthenocarpy is found in tomato and other species in which the processes of pollination and fertilization depend on narrow environmental limits. Id. In facultative parthenocarpy, seeded or seedless fruits are produced in response to environmental stimuli. Id. For example, the parthenocarpic tomato line "Severianin" from the Gribovskja Experimental Vegetable Station near Moscow, Russia, was found to have the remarkable ability to produce seedless or seeded fruits of similar weight depending on the environmental conditions. Splittstoesser, Walter E., "Temperature influences Parthenocarpic Fruit Production in Tomato", Proc. Plant Growth Regal. Soc. Am (1988). It is also known that naturally occuring parthenocarpic lines have a greater amount of growth-promoting substances in the ovary and as a result, the failure of pollination or lack of seed formation will not prevent the development of fruit.
Many cultivars exhibiting parthenocarpy from around the world have been studied, thus, various sources of parthenocarpy are known. Parthenocarpy is known to be controlled genetically by one or more recessive genes. Many recessive genes controlling parthenocarpy are known. These genes are pat, pat-2, pat-3, pat-4, and pat-5. A short anther (sha) allele has also been found to produce parthenocarpic fruits. A seed development suppressor (sds) allele has also been found which produces normal fruit without seeds or only with a little quantity of very small seeds.
One of the problems with parthenocarpic fruit is that their quality tends to be questionable. For example, parthenocarpic fruit tends to be smaller in size than normal fruit. Also, acidity tends to be lower in parthenocarpic fruit, which has an adverse effect on flavor. Additionally, parthenocarpic fruit, especially tomatoes, frequently suffer from various malformations such as puffiness when produced under low temperature conditions.
The cultivated tomato, Lycopersicon esculentum, is one of the most important vegetable crops in the United States and worldwide, with several million tons being produced each year in the United States alone. The commercial importance of the crop has necessitated a constant effort to improve cultivated varieties.
Several parthenocarpic seedless tomatoes are known. For example, 30% of the tomatoes from the tomato line "Farthest North" have no seed. (Baggett, J. R., et al., Hortsci. 13(5):598 (October 1978); Baggett, J. R., et al., Hortsci. 13(5):599 (October 1978). Approximately 50-70% of the tomatoes from the tomato lines Oregon 11 and Gold Nugget have no seed. (Baggett, J. R., et al., Hortiscience, Alexandria American Society for Horticultural Science 17(6), 984-985 (December 1982). Baggett, J. R., et al., Hortiscience, Alexandria, Va.: American Society for Horticultural Science, 20(5), 957-958 (October 1985)). Furthermore, one of the problems with these seedless tomatoes is that no one can determine if the tomato is seedless without first cutting into the tomato. Therefore, prior approaches for obtaining seedless tomatoes have yielded a certain percentage of fruit that do not contain seeds. This is not a practical or commercially beneficial approach for obtaining seedless fruit.
A substantially seedless tomato is not presently commercially available. A need for such a tomato exists, in particular, such a tomato of good quality especially for individuals on strict dietary restrictions who cannot eat food products containing seeds. For example, individuals recovering from surgery to repair a ruptured portion of their gastrointestinal tract typically cannot eat foods that contain seeds. The problem is that these seeds may become trapped in the sutures in the repaired area of the gastrointestinal tract and thereby impair the healing process. If the wall of the gastrointestinal tract does not adequately heal, a further rupture could occur.
Moreover, substantially seedless tomatoes would be beneficial in the food preparation and process products industries. For example, completely seedless tomatoes would make the preparation of certain products such as tomato sauce and tomato paste more efficient and less costly because the seeds would not need to be removed prior to processing.
Therefore, one object of the present invention is to provide a substantially seedless parthenocarpic tomato that exhibits good quality. A second object of the present invention is to provide a method for producing said seedless tomatoes.